1. Field of the Invention
This invention relates to method and apparatus for the storage, retrieval, and loading of units of data storage medium, and particularly to method and apparatus for the storage, retrieval, and loading of cartridges of data storage medium, such as magnetic tape.
2. Prior Art and Other Considerations
A data processing system includes a central processing unit which operates on data stored in a memory. To varying degrees, all data processing systems have central or on-board memory devices which give the central processing unit essentially immediate access to the data stored therein. The cost of such central memory is fairly significant, with the result that data has long been stored on storage media, one form of which being magnetic tape. The storage medium is traditionally provided in a unit, such as a reel or cartridge. The computer system reads data from the storage medium, and writes data to the storage medium, in conjunction with a peripheral media-handling device, such as a tape drive, that physically handles the storage medium. In this regard, the computer system, through an appropriate interface device or chip, communicates with the peripheral device to request the read/write operations conducted by the peripheral device and to control the transfer of data between the computer and the peripheral device.
Large computer systems typically operate in conjunction with a number of peripheral media-handling devices. For example, a host computer might access four, five, or more tape drives. Each peripheral media-handling device can only operate on one unit of storage medium at any given time, which unit is said to be loaded into or mounted on the media-handling peripheral. However, a plurality of units, perhaps hundreds, can be associated with one or more peripheral, and mounted or loaded thereon at the proper time. To this end, sizable libraries consisting of racks for storing the large number of units, such as reels, have traditionally been located proximate the peripheral devices.
At the birth of the information storage and retrieval industry,.magnetic tape reels were manually mounted on tape drives by human operators. Although the data processing system functioned in fractions of seconds, the human selection and manipulation of the tape reels was significantly longer, which occasioned considerable delays. Such was particularly true when the operator had to locate one reel out of myriads, visually verify the selection, and mount the reel on the proper tape drive.
Automated tape libraries were developed to expedite the selection and loading of magnetic tape reels. One such automated tape library resembles an elongated rectangular room. Racks of tape reels are provided at selected locations along the interiors of the opposing elongated walls. An interior track runs the length of the room between the parallel racks. A reel retrieval/loading device is mounted on a carriage that travels along the track, and is translatable along two rectangular axes in addition to the third axis of the track. The retrieval/loading device is automatically controlled to locate and engage a selected reel in a Cartesian coordinate system, and then transports the selected reel to a target on one of a plurality of tape drives. The tape drives are located along the exterior wall of the room at windows provided for access to the drives. The retrieval/loading device automatically mounts the selected reel on the target tape drive.
Another prior art configuration for a storage library features a cylindrical room, with storage racks provided along the interior of the circular wall and a plurality of peripheral devices located along the exterior at windows. The retrieval/loading device is positioned in the center of the room, and is operated in a cylindrical coordinate fashion.
The prior art retrieval/loading devices are complicated mechanisms. The retrieval/loading devices require not only structure for translation along three axes, but also entail structure for precise engagement of the units of storage medium. Although the complex structure of these prior art retrieval/loading devices invite considerable maintenance and repair, the location of the devices does not facilitate ready access or removal. Moreover, replacement of the retrieval/loading device is very costly from the standpoint of labor and down time.
The complex structure of prior retrieval/loading device for libraries results in large part from the number of mechanisms required to perform specialized operations. As an example, once a unit of storage medium is engaged, a separate locking mechanism is required lest the unit be mishandled or dropped. Mishandling can damage the unit and perhaps cause errors on the storage medium Dropping the unit can not only damage the unit, but can also obstruct operation of the retrieval/loading device.
Magnetic tape cartridges have recently become popular as a unit of storage medium, particularly 8 mm magnetic tape cartridges (as used herein, the term "cartridge" also refers to magnetic tape cassettes). Advantageously, magnetic tape cartridges facilitate economic and compact storage of data. However, an automated library system which overcomes the aforementioned problems of prior art libraries has heretofore not been provided.
In view of the foregoing, it is an object of the present invention to provide method and apparatus for simply and securely engaging and disengaging a magnetic tape cartridge.
Another object of the present invention is the provision of an automated library system wherein a retrieval/loading device is easily accessible.
An advantage of the present invention is the provision of a modular and replaceable retrieval/loading device for an automated library system.
Another advantage of the present invention is the provision of a retrieval/loading device and method of operation therefor that facilitates a multiplicity of operations.